1. Field of the Invention
The present invention relates to an endless transmission belt for a V-belt type continuously variable speed transmission.
2. Description of the Prior Art
Japanese Laid-Open Patent application Gazette (Kokai) No. 61-79044 discloses an endless transmission belt for transmitting torque between a pair of pulleys each having a contact surface formed of two coaxial and opposite surfaces of circular cones of a continuously variable speed transmission. This known endless transmission belt comprises a plurality pairs of first and second metallic blocks in which each block being formed in the shape of a trapezoidal plate having opposite inclined side edges partly or entirely provided with inclined contact surfaces to be in contact with the contact surfaces of the pulleys and provided with a through hole or an opening having a predetermined lateral size practically in the center portion thereof with respect to the width, each pair of first and second metallic blocks being placed with the respective first side walls thereof in contact with each other; and an endless chain belt formed by linking a set of thin link plates having a width substantially corresponding to the width of the through hole or the opening formed in the metallic block and connecting the set of thin link plates at the opposite ends to those of the adjacent groups of thin link plates, and passed through the through holes or openings of the metallic blocks, and pairs of pins engaging grooves formed on walls contiguous to the through hole or the opening in the respective second side walls of the pair of first and second metallic blocks, so as to hold the pair of first and second metallic blocks therebetween so that the plurality of first and second metallic blocks are held on the endless chain belt of the link plates.
In this known endless transmission belt, the metallic blocks are held by the respective opposite ends of the pins which extend across the endless chain belt and allow the pivotal motion of the link plates thereon. Therefore, when the metallic blocks engage the pulley during the power transmitting operation of the endless transmission belt, all the stresses such as a force which acts radially outward on the metallic blocks and a force which acts on the metallic block due to the interaction of the link plates and the metallic block for power transmission are concentrated at the both opposite ends of each pin to bend the pin in a curve. Consequently, the link plates on the opposite sides of the parallel arrangement of the link plates are loaded more heavily than the rest of the link plates and hence the link plates located on the opposite outer sides of the parallel arrangement of the link plates in the endless chain belt are more liable to be abraded than the rest of the link plates and in the worst case, are broken. Furthermore, the both opposite ends of the pins are abraded more heavily than the middle portions.
Still further, in an endless transmission belt in which the endless belt is passed through through holes respectively formed in the center portion of respective metallic blocks, a radially inward stress is applied to the lower side of each metallic block by which the respective through hole is closed, to strain the lower side of the same when the metallic block engages the pulley at the time when the inclined contact surfaces formed in the opposite side edges of the metallic block contact to the contact surfaces of the pulleys and pressure is applied thereto. (Refer to U.S. Pat. No. 4,512,754).